1. Field of the Invention
The present invention relates to an image sensing apparatus which takes an image and corrects a distortion of the image.
2. Description of Related Art
There are widely used image sensing apparatuses which generate images in which a shake due to a movement of the image sensing apparatus or a subject (human body or other object to be imaged) is reduced. Some of the image sensing apparatuses includes an image processing unit which detects a shake and generates an image in which the shake is reduced.
As one type of the above-mentioned shake, there is a so-called focal plane distortion (hereinafter may be referred to as a “distortion” simply). The focal plane distortion is a type of distortion that may occur, for example, in a CMOS (Complementary Metal Oxide Semiconductor) image sensor or the like in which exposure and reading of charge are restricted for each pixel (which is a so-called X-Y addressing type). In particular, the distortion may occur because of different exposure timing for each pixel row.
A concrete example of the focal plane distortion is illustrated in FIGS. 1A to 1E, which are schematic diagrams illustrating a focal plane distortion. FIG. 1A is a schematic diagram of an image obtained when an image sensing apparatus is stopped. FIG. 1B is a schematic diagram of the image obtained when the image sensing apparatus is moved in parallel from the left to the right or is rotated in the pan direction from the left to the right. FIG. 1C is a schematic diagram of the image obtained when the image sensing apparatus is moved in parallel from the right to the left or is rotated in the pan direction from the right to the left. FIG. 1D is a schematic diagram of the image obtained when the image sensing apparatus is moved in parallel upward or is rotated in the tilt direction upward. FIG. 1E is a schematic diagram of the image obtained when the image sensing apparatus is moved in parallel downward or is rotated in the tilt direction downward. Note that it is supposed that the image sensing apparatus performs image sensing (exposure) from the uppermost pixel row to the lower pixel row sequentially and that the subject S is stopped. In addition, FIGS. 1B to 1E illustrate the cases where constant movements of the image sensing apparatus occur during the image sensing period (during the entire exposure period of the image).
As illustrated in FIG. 1A, the image 100 is obtained when the image sensing apparatus is stopped, and a subject S is positioned in the center of the image 100. In this situation, if each movement of the image sensing apparatus occurs, the image obtained by image sensing becomes as follows. As illustrated in FIGS. 1B to 1E, the subject S in the image is distorted to move in the direction that is opposite to the movement of the image sensing apparatus, and the distortion is larger in the lower portion. For instance, if the image sensing apparatus moves horizontally from the left to the right as illustrated in FIG. 1B, the subject S in the obtained image 101 is distorted to move to the left, and the distortion is larger in the lower portion. In addition, if the image sensing apparatus moves horizontally from the right to the left as illustrated in FIG. 1C, the subject S in the obtained image 102 is distorted to move to the right, and the distortion is larger in the lower portion. In addition, if the image sensing apparatus moves vertically upward as illustrated in FIG. 1D, the subject S in the obtained image 103 is distorted and elongated downward. In addition, if the image sensing apparatus moves vertically downward as illustrated in FIG. 1E, the subject S in the obtained image 104 is distorted and shortened upward. These distortions occur because the exposure timing in the image sensing is earlier for upper pixel rows and is later for lower pixel rows as described above.
As a method of distortion correction process for reducing the focal plane distortion described above, there is proposed a method of detecting a movement of the image sensing apparatus and performing distortion correction process for correcting a distortion corresponding to the movement on the image obtained from the image sensor, so as to obtain an image with reduced distortion, for example.
However, when the distortion correction process is performed by the above-mentioned image processing, there may be the case in which wrong distortion correction process is performed. If the wrong distortion correction process is performed, the correction process may be performed on an image with no distortion, for example. As a result, a distortion may oppositely occur in an output image, resulting in a problem of degradation of the output image.